The antiglare film and the antireflection film used in an image display device such as a cathode-ray tube display device (CRT), a plasma display panel (PDP) and a liquid crystal display device (LCD), are generally disposed on the outermost surface of the display in which the reflectance is reduced by making use of the optical interference principle to prevent the reduction of contrast ascribable to the reflection of exterior light or to prevent the superposing of an image.
The display having disposed on the outermost surface thereof an antiglare film or an antiglare and antireflection film is prevented from the reduction of contrast ascribable to the reflection of external light or from the superposing of an image. However, on the other hand, when the display is viewed from the oblique direction, the black display shows white-tinted black or gray and this is disliked because the display quality decreases. This phenomenon is called bad sinking of black, loosened black or bad white tinting. This is a phenomenon such that light greatly scatters on the surface due to asperities formed on the film surface so as to impart antiglare property and the scattered light intermingles into the area which is originally viewed black, to show the area whitish. This causes worsening of the contrast and badly impairs the high-grade effect of the display. This may be overcome by reducing the numbers of asperities on the film surface, however, if the case is so, the white tinting may be improved but the antiglare property decreases. As a result of extensive investigations by the present inventors on the protrusion height and the number of protrusions, it has been found that as long as the antiglare property is the same, formation of a smaller number of large protrusions on the film surface is more advantageous in view of the white tinting than the formation of a large number of small protrusions.
On the other hand, when an image is viewed through an antiglare film or an antiglare and antireflection film, the transmitted image clarity deteriorates. This occurs because the transmitted light from picture elements is bent by the asperities on the film surface and thereafter, enters an eye. The transmitted image clarity can be measured by an image clarity measuring machine prescribed in JIS K7105-6.6. If the transmitted image clarity is bad, the image blurs on viewing.
As a result of studies, it has been found that the transmitted image clarity is determined by the protrusion height of asperities on the film surface and as the protrusion height is smaller, the clarity is higher. Asperities having a protrusion height in excess of a predetermined height cannot be used for a display directed to a higher grade. In other words, in the case of conventional antiglare film or antiglare and antireflection film, the attempt to attain both high transmitted image clarity and improved white tinting at the same time while maintaining the antiglare property cannot succeed only by the control of the protrusion height and the number of protrusions.
For compensating the antiglare property of the antiglare film, an antireflection function may be imparted to the film to reduce the light quantity of an image on a display. When the protrusion height on the film surface is set to a height capable of satisfying the transmitted image clarity and additionally an antireflection function is imparted, the number of protrusions can be more reduced than in the case of having no antireflection function. However, this technique still cannot compensate for the white tinting and the deterioration in contrast.